The present invention relates to a rotary slide type mechanical pencil in which an axial body member is rotated to advance and extend a slider holding a lead to a writing position.
U.S. patent application Ser. No. 25,525 filed on Mar. 30, 1979, issued on Aug. 19, 1980 as U.S. Pat. No. 4,218,153 and entitled "Mechanical Pencil", directed to a rotary slide type mechanical pencil of this general type, was previously filed by the present applicant. More particularly, this patent relates to a mechanical pencil in which the pencil body is divided into front and rear axial bodies. When either axial body is rotated relative to the other, a chuck tightening member is advanced and engages with a lead chuck to grip the lead and thereafter the chuck clamping the lead is advanced. The mechanical pencil further includes a lead holding retainer disposed in front of the chuck and a slider movable through a predetermined fixed distance. With this construction, when either of the axial bodies is rotated, the tightening member is advanced and engages with the chuck and thereafter the lead clamped by the chuck is further advanced with the tightening member engaged with the chuck whereby lead is supplied from an opening of the slider which has been advanced and stopped at the advanced position during a single continuous rotation. To retract the slider, the axial body is rotated in the opposite direction. However, in this mechanical pencil, when the lead extends from the opening of the slider and the slider is retracted when this lead has not been written with to wear out the lead, during the next use additional lead is supplied adding to the extended lead length. Thus, excessive lead length is added to the lead held by the slider. This tends to cause a lead breakage and results in inconvenient and excessive operation. If the pencil is so designed that in the retracted state the front end of the slider and the front end of the mouth member, that is, the forward-most end of the pencil body, coincide with each other while at the same time the rear end of the slider abuts the chuck so that the chuck is disposed forwardly, it is possible to avoid the above-noted defect and to retract the excessive lead into the slider by pressing the end of the lead against a solid surface. In this case, since the lead is not gripped by the chuck, the lead is easily retracted into the slider.
However, with such a design or construction, there is yet another problem. Since the position of the chuck for writing is further forward than the position of the chuck in the retracted state, the lead extends forwardly from the opening of the slider a length equal to the difference between these positions. In this case, the slider cannot be retracted into the mouth during writing. This is due to the fact that the rear end of the slider abuts against the chuck so that the front portion of the slider is left extending from the opening of the mouth member. This causes the paper to be torn by the stopped slider during continuous writing.
In order to remedy the above-noted defects, it is an object of the present invention to provide a rotational slide mechanical pencil in which excessive lead supply from a front end of the slider is prevented when the slider is advanced from the retracted state to the writing state while at the same time the slider can be fully retracted into the mouth member in the writing state.